Scientific accurate quantification of topographic feature of watershed is one of the key issues in establishing an extensively applicable model for prediction of soil erosion on a watershed scale on Loess Plateau. Based on the fractal theory and with the aid of the GIS technology and multianalysis method, coupling relationship between sediment yield from rainfall erosion and topographic features was studied in the Chabagou watershed, which lies on Loess Plateau. Results show that the coupling relationship model, into which fractal information dimension of topographic feature of watershed is introduced, can simplify the relationship between runoff and sediment yield that varies from branch to branch of the Chabagou watershed to a uniform mathematic expression. As a whole, the relative error of the prediction of sediment transport modulus of the Xizhuang and Shejiagou watersheds using the model is low. It is feasible and reliable to use fractal information dimension of topographic features of watershed as an index to quantify topographic features of watershed, which is one of the important influencing factors in establishing models for soil erosion prediction on a watershed scale.